One of the most important elements in traditional high quality guitars of the type described generally above is the sound board portion of the top member. Vibrations from the strings are transmitted to the sound board and through the bridge. Therefore, the construction of the sound board has a great deal of influence on the overall acoustic performance of the guitar.
In classical guitars, fine grained soft woods, e.g., spruce, red cedar or red wood, are frequently used as a sounding board material for their exquisite tonal and visual qualities. However, wooden instruments are inherently vulnerable to the elements, particularly humidity, moisture and heat. The stiffness of a wood sounding board may vary with changes in humidity. For example, wood sounding boards are subject to sinking, or transversing inward, bowing, creeping, or developing ripples under conditions of high humidity and deforming under string tension. The tendency of wood to crack under hot, dry conditions introduces further problems. Since the physical characteristics of wood vary, it is difficult to manufacture instruments which have uniform sound producing qualities.
Also, separate structural reinforcements, e.g., braces and neck blocks, must generally be provided to compensate for string tension in wood instruments. The braces are also used to distribute the string vibrations received by the bridge over the top member and to supply structural reinforcement to the areas near any sound holes located in the top member. These reinforcements add considerably to the manufacturer's cost and weight of such an instrument, and are known to affect the tone.
To compensate for many of the problems associated with wood instruments, it has been proposed in the past to make top members and other guitar components of composite materials. The term "composite materials" means materials made chiefly of two or more weather resistant non-wood components, such as carbon fibers embedded in an epoxy resin matrix with the fibers either being arranged randomly, unidirectionally or woven into a fabric. However, sound board portions of composite material top members often do not have the same desirable tonal and other response qualities as wooden sound boards.
In attempts to address this problem some prior art composite top members utilize a laminated construction having at least a pair of composite material layers with a core layer of wood, or perhaps some other material, e.g., an aramid material, bonded between. (Aramids are defined by the Merriam-Webster Collegiate Dictionary, and for purposes of this application, as any of a group of lightweight but very strong heat-resistant synthetic aromatic polyamide materials that are fashioned into fibers, filaments, or sheets and used especially in textiles and plastics.) The more freely the core layer is allowed to vibrate, the better the tonal quality of the instrument and the more closely the sound board portion simulates the acoustical performance of wood. However, in prior laminated sound boards with wooden or other core layers, the core layer extends all the way to the sidewall of the instrument body, so that adjacent the sidewalls, the composite material layers clamp against the core layer and restrict core vibrations in much the same way a vibrating cymbal would be restricted if held by its outer edges.
Moreover, to reduce weight, prior laminated composite top members are often manufactured from relatively thin material. As a result, the top member is initially flexible and a considerable number of braces are required to supply structural reinforcement to the top member, especially in areas near any sound hole or holes located in the sound board.
There is, therefore, a need for an improved top member for the body of an acoustical or acoustical/electric stringed instrument.